Methods for fabricating strained gate-all-around semiconductor devices by fin oxidation using an undercut etch-stop layer

ABSTRACT

Strained gate-all-around semiconductor devices formed on globally or locally isolated substrates are described. For example, a semiconductor device includes a semiconductor substrate. An insulating structure is disposed above the semiconductor substrate. A three-dimensional channel region is disposed above the insulating structure. Source and drain regions are disposed on either side of the three-dimensional channel region and on an epitaxial seed layer. The epitaxial seed layer is composed of a semiconductor material different from the three-dimensional channel region and disposed on the insulating structure. A gate electrode stack surrounds the three-dimensional channel region with a portion disposed on the insulating structure and laterally adjacent to the epitaxial seed layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.13/629,135, filed on Sep. 27, 2012, the entire contents of which arehereby incorporated by reference herein.

TECHNICAL FIELD

Embodiments of the invention are in the field of semiconductor devicesand, in particular, strained gate-all-around semiconductor devicesformed on globally or locally isolated substrates.

BACKGROUND

For the past several decades, the scaling of features in integratedcircuits has been a driving force behind an ever-growing semiconductorindustry. Scaling to smaller and smaller features enables increaseddensities of functional units on the limited real estate ofsemiconductor chips. For example, shrinking transistor size allows forthe incorporation of an increased number of memory devices on a chip,lending to the fabrication of products with increased capacity. Thedrive for ever-more capacity, however, is not without issue. Thenecessity to optimize the performance of each device becomesincreasingly significant.

In the manufacture of integrated circuit devices, multi-gatetransistors, such as tri-gate transistors, have become more prevalent asdevice dimensions continue to scale down. In conventional processes,tri-gate transistors are generally fabricated on either bulk siliconsubstrates or silicon-on-insulator substrates. In some instances, bulksilicon substrates are preferred due to their lower cost and becausethey enable a less complicated tri-gate fabrication process. In otherinstances, silicon-on-insulator substrates are preferred because of theimproved short-channel behavior of tri-gate transistors.

Silicon-on-insulator substrates, formed either by global isolation orlocal isolation, may also be used to fabricate gate-all-around devices.Many different techniques have been attempted to fabricate suchthree-dimensional isolated channel devices. However, significantimprovements are still needed in the area of isolation formation forsuch semiconductor devices.

In another aspect, many different techniques have been attempted toimprove the mobility of transistors. However, significant improvementsare still needed in the area of electron and/or hole mobilityimprovement for semiconductor devices.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B illustrate cross-sectional views of various operationsin a method of fabricating a semiconductor device.

FIGS. 2A-2C illustrate cross-sectional views of various operations in amethod of fabricating a semiconductor device, in accordance with anembodiment of the present invention.

FIG. 3A illustrates a three-dimensional cross-sectional view of ananowire-based semiconductor structure, in accordance with an embodimentof the present invention.

FIG. 3B illustrates a cross-sectional channel view of the nanowire-basedsemiconductor structure of FIG. 3A, as taken along the a-a′ axis, inaccordance with an embodiment of the present invention.

FIG. 3C illustrates a cross-sectional spacer view of the nanowire-basedsemiconductor structure of FIG. 3A, as taken along the b-b′ axis, inaccordance with an embodiment of the present invention.

FIGS. 4A-4J illustrate cross-sectional views of various operations in amethod of fabricating a semiconductor device, in accordance with anembodiment of the present invention.

FIGS. 5A-5J illustrate cross-sectional views of various operations inanother method of fabricating a semiconductor device, in accordance withan embodiment of the present invention.

FIGS. 6A-6G illustrate cross-sectional views of various operations inanother method of fabricating a semiconductor device, in accordance withan embodiment of the present invention.

FIG. 7 illustrates a computing device in accordance with oneimplementation of an embodiment of the invention.

DESCRIPTION OF THE EMBODIMENTS

Strained gate-all-around semiconductor devices formed on globally orlocally isolated substrates are described. In the following description,numerous specific details are set forth, such as specific integrationand material regimes, in order to provide a thorough understanding ofembodiments of the present invention. It will be apparent to one skilledin the art that embodiments of the present invention may be practicedwithout these specific details. In other instances, well-known features,such as integrated circuit design layouts, are not described in detailin order to not unnecessarily obscure embodiments of the presentinvention. Furthermore, it is to be understood that the variousembodiments shown in the Figures are illustrative representations andare not necessarily drawn to scale.

One or more embodiments of the present invention are directed to the useof or inclusion of an undercut (UC) control layer during semiconductordevice fabrication. For example, an undercut control layer may be usedto integrate strain in under fin oxidation (UFO) or silicon-on-insulator(SOI) or silicon germanium-on-insulator (SiGeOI) FIN formation toenable, e.g., enhanced channel strain formation. UFO-based structuresmay be referred to as locally isolated from an underlying substrate,while SOI-based structures may be referred to as globally isolated froman underlying substrate. Embodiments of the present invention may besuitable for both such locally and globally isolated structures. In oneor more specific embodiment, an epitaxial seeding layer is retained forepitaxial structure formation. The epitaxial seeding layer may beretained or later removed in subsequent process operations.

In general, solutions described herein may be suitable for straining apartially or entirely isolated device. The isolation may be achieved ormay be a result of global isolation (SOI) or local isolation (UFO)where, in either case, an intervening insulating layer is disposedbetween a channel region an underlying bulk semiconductor substrate. Theintervening dielectric layer may be fabricated by, e.g., under finoxidation (UFO), buried oxide formation (BOX), or replacementdielectrics, or may included in a starting substrate.

Perhaps more specifically, one or more embodiments of the presentinvention are directed to integrating gate-all-around devices. As such,high performance, low leakage transistor technology approaches aredescribed herein. Difficulty in increasing electron and hole mobilitysimultaneously when the same channel material is used for both the NMOSand PMOS is also addressed herein. Device performance may be enhancedusing strain solutions, higher mobility channel approaches, or highermobility channel orientations.

Approaches described herein may be used to address issues of carriermobility in channel materials of semiconductor devices. For example, inan embodiment, an undoped silicon (Si) material channel is provided fora FIN structure. The Si FIN is formed on an SiO₂-based substrate to takeadvantage of a fully undoped channel (e.g., with no subFIN leakage) andminimized gate induced drain leakage (GIDL) or junction leakage.However, Si cannot typically be grown epitaxially on a SiO₂ buriedlayer. Furthermore, if a UFO technique is used to form an oxide layerunder the FIN or if an SOI wafer is used, then integration of source ordrain (S/D) stressors to transfer the strain to the channel region (suchas epitaxial SiGe used to strain a silicon channel region) may becomplicated. For example, an undercut process (e.g., removal of startingS/D material) may be inhibited by the restriction of not being able toexpose the SiO₂ buried layer (or UFO or SiGeOI) since the epitaxiallygrown stressor may not nucleate and grow on top of the oxide. As such,integrating a maximum available S/D induced strain on an isolated FINwith a buried oxide may be very challenging.

Conventional approaches to integrating epitaxial channel strainingregions may include performing a shallow undercut to leave a thin Silayer (or other epitaxial nucleation layer) disposed over a local orglobal buried oxide in order to enable epitaxial stressor nucleation.Such an approach may not be optimal since any capacity for inducedstrain will likely be reduced considering the S/D epitaxial volume islimited. Also, with such a controlled undercut technique may not permitintegration of epitaxial material to grow in a tip region of afabricated device which otherwise brings straining features very closeto a channel region for maximum the stress transfer.

To exemplify the above identified issues with conventional approaches,FIGS. 1A and 1B illustrate cross-sectional views of various operationsin a method of fabricating a semiconductor device. Referring to FIG. 1A,a semiconductor structure 100 includes a semiconductor body 106, such asa silicon layer, disposed on an insulating layer 104, such as global orlocal insulating layer, on a substrate 102, such as a bulk siliconsubstrate. A gate electrode 108, such as a polysilicon placeholder gateelectrode with hardmask 110 and spacers 112, is disposed above thesemiconductor body 106. Referring to FIG. 1B, exposed portions of thesemiconductor body 106 are recessed to form recessed regions 114. Therecessed regions 114 reduce the thickness of the semiconductor body 106,but do not expose the underlying insulating layer 104. The recessedregions 114 provide a location for epitaxial nucleation for, e.g.,subsequent source and drain stressor formation. For example, silicongermanium (SiGe) may subsequently be grown on recessed portions 114 ofthe semiconductor body 106 in order to provide stress to the channelregion of the semiconductor body 106 under the gate electrode 108.

However, referring again to FIG. 1B, since a portion of thesemiconductor body must be preserved in regions 114 in order to providea nucleation site (which is not otherwise provided by insulating layer104) only a shallow recess may be achieved. Additionally, there islittle to no undercut of the portion of the semiconductor body 106 underthe gate electrode 108 that would otherwise permit formation ofepitaxial regions in closer proximity to the active channel region ofsemiconductor body 106. As such, the shallow recessing and minimalundercut may hinder the extent of allowed epitaxial volume under thegate electrode 108, possibly limiting the amount of stress transferredto the channel region.

As such, one or more embodiments are directed to enabling integration ofstrain on UFO/SiGeOI FINs by the implementation of an etch stop layer(e.g., where the SiGe is buried) that is sacrificial and maysubsequently be removed to provide a gate-all-around or/andcontact-all-around structure. The deposition of a sacrificial undercutetch stop layer or sacrificial top layer buffer and its removal in thechannel and or S/D regions is described in greater detail below.

To exemplify the above solutions, FIGS. 2A-2C illustrate cross-sectionalviews of various operations in a method of fabricating a semiconductordevice, in accordance with an embodiment of the present invention.Referring to FIG. 2A, a semiconductor structure 200 includes asemiconductor body 206, such as a silicon layer, disposed on an undercutetch stop layer 205, such as a silicon germanium etch stop layer. Theundercut etch stop layer 205 is disposed on insulating layer 204, suchas global or local insulating layer, on a substrate 202, such as a bulksilicon substrate. A gate electrode 208, such as a polysiliconplaceholder gate electrode with hardmask 210 and spacers 212, isdisposed above the semiconductor body 206. Referring to FIG. 2B, exposedportions of the semiconductor body 206 are removed to expose portions214 of the undercut etch stop layer 205. The portions 214 of theundercut etch stop layer 205 inhibit exposure of the underlyinginsulating layer 204. Furthermore, an extent 215 of undercut underneaththe gate electrode 208 may be achieved since an overetch process may beused to remove portions of the semiconductor body 206.

The portions 214 of the undercut etch stop layer 205 also provide alocation for epitaxial nucleation for, e.g., subsequent source and drainstressor formation. For example, epitaxial regions 216 such as silicongermanium (SiGe) epitaxial regions may subsequently be grown on portions214 of the undercut etch stop layer 205, adjacent to the remainingportion of the semiconductor body 206, as depicted in FIG. 2C. Theepitaxial regions 216 may be incorporated to provide stress to thechannel region of the semiconductor body 206 under the gate electrode208.

Although FIGS. 2A-2C illustrate the concepts involved in one or moreembodiments of the present invention, more elaborate approaches may alsobe used to fabricate semiconductor devices that benefit from the use ofan undercut etch stop layer. For example, in FIGS. 2A-2C, an interveninginsulating layer (e.g., layer 205) has already been formed (as is alsothe case for the process scheme described in association with FIGS.6A-6G below) prior to formation of a semiconductor body layer (e.g.,layer 206). In other embodiments, such as the case for the processschemes described in association with FIGS. 4A-4J and 5A-5J below, anintervening insulating layer is formed subsequent to semiconductor bodyformation. Furthermore, in FIGS. 2A-2C, a gate electrode or placeholderelectrode is formed prior to recessing of the semiconductor body layer.However, in other embodiments, such as the case for the process schemesdescribed in association with FIGS. 4A-4J, 5A-5J and 6A-6G below, a gateelectrode is fabricated following recessing of a semiconductor bodylayer, enabling formation of gate-all-around semiconductor devices.

Referring again to FIGS. 2A-2C, by using a buried semiconductor layer asan etch stop, then undercut processing may be engineered to maximizevolume and under the gate (XUD) control. An optimum available strain mayas such be transferable to the corresponding channel region. In one suchembodiment, a structure that integrates strained Si FIN on a UFO orSiGeOI substrate is thus achievable. One or more of the process flowsdescribed herein, or the resulting structures and devices may beapplicable to tri-gate and/or FIN-FET transistors for, e.g., 14nanometer and smaller process nodes. Embodiments of the invention mayinvolve depositing a Si FIN on a SiGe sacrificial buffer layer andsubsequently selectively removing the SiGe buffer layer to ultimatelyprovide a Si FIN gate-all-around or contact-all-around structure.

In another aspect, the approach described in association with FIGS.2A-2C may be used in a more complex integration scheme to fabricatenanowire-based devices. For example, FIG. 3A illustrates athree-dimensional cross-sectional view of a nanowire-based semiconductorstructure, in accordance with an embodiment of the present invention.FIG. 3B illustrates a cross-sectional channel view of the nanowire-basedsemiconductor structure of FIG. 3A, as taken along the a-a′ axis. FIG.3C illustrates a cross-sectional spacer view of the nanowire-basedsemiconductor structure of FIG. 3A, as taken along the b-b′ axis.

Referring to FIG. 3A, a semiconductor device 300 includes one or morevertically stacked nanowires (304 set) disposed above a substrate 302.Embodiments herein are targeted at both single wire devices and multiplewire devices. As an example, a three nanowire-based devices havingnanowires 304A, 304B and 304C is shown for illustrative purposes. Forconvenience of description, nanowire 304A is used as an example wheredescription is focused on only one of the nanowires. It is to beunderstood that where attributes of one nanowire are described,embodiments based on a plurality of nanowires may have the sameattributes for each of the nanowires.

Each of the nanowires 304 includes a channel region 306 disposed in thenanowire. The channel region 306 has a length (L). Referring to FIG. 3B,the channel region also has a perimeter orthogonal to the length (L).Referring to both FIGS. 3A and 3B, a gate electrode stack 308 surroundsthe entire perimeter of each of the channel regions 306 of nanowires304C and 304B. In one embodiment, an etch stop semiconductor layer 390portion (described in greater detail below) is not present under thechannel region 306 of nanowire 304A, and the device 300 is thus agate-all-around device with respect to the first nanowire 304A. Inanother embodiment, however, the etch stop semiconductor layer 390portion is present under the channel region 306 of nanowire 304A, andthe device 300 is thus not a gate-all-around device with respect to thefirst nanowire 304A. The gate electrode stack 308 includes a gateelectrode along with a gate dielectric layer disposed between thechannel region 306 and the gate electrode (not shown).

Referring again to FIG. 3A, each of the nanowires 304 also includessource and drain regions 310 and 312 disposed in the nanowire on eitherside of the channel region 306. A pair of contacts 314 is disposed overthe source/drain regions 310/312. Referring to both FIGS. 3A and 3B,pair of contacts 314 is disposed over the source/drain regions 310/312.In one embodiment, an etch stop semiconductor layer 390 portion(described in greater detail below) is not present under the source ordrain region 310 or 312 of nanowire 304A, and the device 300 is thus acontact-all-around device with respect to the first nanowire 304A. Inanother embodiment, however, the etch stop semiconductor layer 390portion is present under the source or drain region 310 or 312 ofnanowire 304A, and the device 300 is thus not a contact-all-arounddevice with respect to the first nanowire 304A.

Referring again to FIG. 3A, in an embodiment, the semiconductor device300 further includes a pair of spacers 316. The spacers 316 are disposedbetween the gate electrode stack 308 and the pair of contacts 314. Asdescribed above, the channel regions and the source/drain regions are,in at least several embodiments, made to be discrete. However, not allregions of the nanowires 304 need be, or even can be made to bediscrete. For example, referring to FIG. 3C, nanowires 304A-304C are notdiscrete at the location under spacers 316. In one embodiment, the stackof nanowires 304A-304C have intervening semiconductor material 318 therebetween, such as silicon germanium intervening between siliconnanowires, or vice versa. In one embodiment, the bottom nanowire 304A isstill in contact with an etch stop semiconductor layer 390 portion.Thus, in an embodiment, a portion of the plurality of vertically stackednanowires under one or both of the spacers is non-discrete.

The etch stop semiconductor layer 390 may be a layer (or remnantsthereof) such as the etch stop layer 205 described in association withFIGS. 2A-2C. In one embodiment, the etch stop semiconductor layer 390 iscomposed of silicon germanium and the overlying nanowire 304A iscomposed of (or at least is initially composed of) silicon. In anotherembodiment, the etch stop semiconductor layer 390 is composed of siliconand the overlying nanowire 304A is composed of (or at least is initiallycomposed of) silicon germanium. In an embodiment, portions of thesemiconductor layer 390 are removed under the channel region of nanowire304A and a gate-all-around structure may be formed. In an embodiment,portions of the semiconductor layer 390 are removed under the source anddrain regions of nanowire 304A and a contact-all-around structure may beformed. In an embodiment, portions of the semiconductor layer 390 areremoved under the channel and the source and drain regions of nanowire304A and both a gate-all-around structure and a contact-all-aroundstructure may be formed. The etch stop semiconductor layer 390 may be alayer (or remnants thereof) may be used to seed growth of epitaxialregions thereon. For example, the etch stop semiconductor layer 390, atsome point, may be used to grow epitaxial straining source and drainregions.

Thus, in accordance with an embodiment of the present invention, the oneor more nanowires 304A-304C of the semiconductor device 300 areuniaxially strained nanowires. Thus, a semiconductor device may befabricated from a single uniaxially strained nanowire (e.g., 304A) orfrom a plurality of vertically stacked uniaxially strained nanowires(304A-304C), as depicted in FIG. 3A. The uniaxially strained nanowire orplurality of nanowires may be uniaxially strained with tensile strain orwith compressive strain. In an embodiment, a compressively uniaxiallystrained nanowire has a channel region composed of silicon. Thecorresponding compressively uniaxially straining source and drainregions are composed of silicon germanium (Si_(x)Ge_(y), where 0<x<100,and 0<y<100). In another embodiment, a tensilely uniaxially strainednanowire has a channel region composed of silicon germanium(Si_(x)Ge_(y), where 0<x<100, and 0<y<100). The corresponding tensilelyuniaxially straining source and drain regions are composed of silicon.In an embodiment, a PMOS semiconductor device is fabricated from ananowire having the uniaxial compressive strain. In an embodiment, anNMOS semiconductor device is fabricated from a nanowire having theuniaxial tensile strain.

Referring to FIGS. 3A-3C, the semiconductor device 300 further includesa dielectric layer 330 disposed between a bulk substrate 302 and thenanowires 304A-304C. In an embodiment, the dielectric layer 330 iseffectively continuous across a substrate 302 and is a global insulatinglayer. In one embodiment, the dielectric layer 330 is composed of adielectric material such as, but not limited to, silicon dioxide,silicon oxy-nitride or silicon nitride. In another embodiment, thenanowires 304A-304C are isolated from a bulk substrate 302 by anisolation pedestal, e.g., they are locally isolated. The isolationpedestal may be composed of a material suitable to electrically isolateat least a portion, if not all, of the nanowire 304A from the bulksubstrate 302. For example, in one embodiment, the isolation pedestal iscomposed of a dielectric material such as, but not limited to, silicondioxide, silicon oxy-nitride or silicon nitride. In an embodiment, theisolation pedestal is composed of an oxide of the semiconductor materialof the bulk substrate 302.

In an embodiment, the term “isolation pedestal” is used to covey adiscrete isolation structure formed at a given time, e.g., a discretestructure formed only under a channel region, or a pair of discretestructures formed only under a pair of source and drain regions, or adiscrete structure formed under a channel region as well as under a pairof source and drain regions. In another embodiment, the term “isolationpedestal” is used to covey a combination of isolation structures formedat different times, e.g., a discrete structure formed under a channelregion in combination with a pair of discrete structures formed, at adifferent time, under a pair of source and drain regions.

Bulk substrate 302 may be composed of a semiconductor material that canwithstand a manufacturing process. In an embodiment, bulk substrate 302is composed of a crystalline silicon, silicon/germanium or germaniumlayer doped with a charge carrier, such as but not limited tophosphorus, arsenic, boron or a combination thereof. In one embodiment,the concentration of silicon atoms in bulk substrate 302 is greater than97%. In another embodiment, bulk substrate 302 is composed of anepitaxial layer grown atop a distinct crystalline substrate, e.g. asilicon epitaxial layer grown atop a boron-doped bulk siliconmono-crystalline substrate. Bulk substrate 302 may alternatively becomposed of a group III-V material. In an embodiment, bulk substrate 302is composed of a III-V material such as, but not limited to, galliumnitride, gallium phosphide, gallium arsenide, indium phosphide, indiumantimonide, indium gallium arsenide, aluminum gallium arsenide, indiumgallium phosphide, or a combination thereof. In one embodiment, bulksubstrate 302 is composed of a III-V material and the charge-carrierdopant impurity atoms are ones such as, but not limited to, carbon,silicon, germanium, oxygen, sulfur, selenium or tellurium. In anotherembodiment, bulk substrate 302 is undoped or only lightly doped.

In an embodiment, the gate electrode of gate electrode stack 308 iscomposed of a metal gate and the gate dielectric layer is composed of ahigh-K material. For example, in one embodiment, the gate dielectriclayer is composed of a material such as, but not limited to, hafniumoxide, hafnium oxy-nitride, hafnium silicate, lanthanum oxide, zirconiumoxide, zirconium silicate, tantalum oxide, barium strontium titanate,barium titanate, strontium titanate, yttrium oxide, aluminum oxide, leadscandium tantalum oxide, lead zinc niobate, or a combination thereof.Furthermore, a portion of gate dielectric layer may include a layer ofnative oxide formed from the outer few layers of the semiconductornanowires 304A-304C. In an embodiment, the gate dielectric layer iscomposed of a top high-k portion and a lower portion composed of anoxide of a semiconductor material. In one embodiment, the gatedielectric layer is composed of a top portion of hafnium oxide and abottom portion of silicon dioxide or silicon oxy-nitride.

In one embodiment, the gate electrode is composed of a metal layer suchas, but not limited to, metal nitrides, metal carbides, metal silicides,metal aluminides, hafnium, zirconium, titanium, tantalum, aluminum,ruthenium, palladium, platinum, cobalt, nickel or conductive metaloxides. In a specific embodiment, the gate electrode is composed of anon-workfunction-setting fill material formed above a metalworkfunction-setting layer.

The contacts 316 are, in an embodiment, fabricated from a metal species.The metal species may be a pure metal, such as nickel or cobalt, or maybe an alloy such as a metal-metal alloy or a metal-semiconductor alloy(e.g., such as a silicide material). In an embodiment, spacers 316 arecomposed of an insulative dielectric material such as, but not limitedto, silicon dioxide, silicon oxy-nitride or silicon nitride.

Semiconductor device 300 may be any semiconductor device incorporating agate, one or more channel regions and one or more pairs of source/drainregions. In an embodiment, semiconductor device 300 is one such as, butnot limited to, a MOS-FET, a memory transistor, or aMicroelectromechanical System (MEMS). In one embodiment, semiconductordevice 300 is a three-dimensional MOS-FET and is a stand-alone device oris one device in a plurality of nested devices. As will be appreciatedfor a typical integrated circuit, both N- and P-channel transistors maybe fabricated on a single substrate to form a CMOS integrated circuit.

Although the device 300 described above is for a single device, e.g., anNMOS or a PMOS device, a CMOS architecture may also be formed to includeboth NMOS and PMOS channel devices disposed on or above the samesubstrate. A plurality of such NMOS devices, however, may be fabricatedto have different semiconductor body heights and/or may be isolated fromor coupled to an underlying bulk substrate. Likewise, a plurality ofsuch PMOS devices may be fabricated to have different semiconductor bodyheights and/or may be isolated from or coupled to an underlying bulksubstrate. Furthermore, additional processing not shown may includeprocessing operations such as back-end interconnect formation andsemiconductor die packaging.

A CMOS architecture may also be formed to include both NMOS and PMOSnanowire-based devices disposed on or above the same substrate.Nanowire/nanoribbon structure may be formed by selective etching ofsacrificial layers from multilayer epitaxial stacks. The epitaxiallayers may be used as a channel or may be selectively removed to form agap for all-around gate structure. The isolation layer under epitaxialwires may provide electrical isolation and form a bottom gap forall-around gate. The simplest CMOS integration scheme employs N/P MOSchannels fabricated with the same material. The process is simpler tofabricate in that it employs a single selective etch. However, asdescribed throughout herein, strain technology may be required to boostdevice performance. For example, when silicon was used for channelmaterial, PMOS is enhanced by compressive stress and NMOS is enhanced bya tensile stress along channel direction to enhance carrier mobility. Inaccordance with an embodiment of the present invention, the uniquefeatures of a starting material stack are exploited to integratedifferent NMOS and PMOS channel materials which are optimized for highermobility. For example, in one embodiment, a sacrificial layer of an NMOSdevice is used as a PMOS channel and a sacrificial layer of a PMOSdevice is used as an NMOS channel. Since the sacrificial layer may beremoved during processing, independent choice of channel materials andoptimization is made possible.

More generally, focusing on a gate-all-around aspect of embodiments ofthe present invention, different approaches are available to provide agate surrounding a channel region or a contact surrounding asource/drain region, or both. One or more embodiments of the presentinvention are directed to a plurality of semiconductor devices havingthree-dimensional bodies or active regions (e.g., fins) formed from abulk substrate, such as a bulk single crystalline silicon substrate. Oneor more of the plurality of devices is subsequently subjected to anunder fin oxidation (UFO, described in greater detail below) process toisolate, or at least restrict, the device from the underlying bulksubstrate. Accordingly, one or more embodiments include fabricationprocesses using a selective (versus global) UFO process to provideselective substrate isolation for targeted devices. However, otherembodiments are directed to a plurality of semiconductor devices havingthree-dimensional bodies or active regions formed on a globallyinsulating substrate.

In a first example utilizing a UFO approach, FIGS. 4A-4J illustratecross-sectional views of various operations in a method of fabricating asemiconductor device, in accordance with an embodiment of the presentinvention. Referring to FIG. 4A, a starting semiconductor structure 400includes semiconductor bodies 406, such as silicon fins, disposed on anundercut etch stop layer 405, such as a silicon germanium etch stoplayer. The undercut etch stop layer 405 is disposed on a substrate 402,such as a bulk silicon substrate. A hardmask layer 410, such as asilicon nitride hardmask layer, is disposed on the semiconductor bodies406. Spacers 412, such as silicon nitride spacers are formed along thesidewalls of the semiconductor bodies 406, as depicted in FIG. 4B, e.g.,by conformal layer deposition and etch back. Referring to FIG. 4C,exposed portions of the substrate 402 are removed to providesemiconductor pedestals 420 underneath the semiconductor bodies 406. Forexample, in the case that the semiconductor bodies 406 are protected bysilicon nitride hardmask and spacers and by a silicon germanium etchstop layer, the semiconductor pedestals 420 may be formed selectivelywithout impacting the semiconductor bodies 406. The semiconductorpedestals 420 are then oxidized to form isolation pedestals 422, asdepicted in FIG. 4D. Oxidation may also occur in the top portion of theremaining substrate 402 and, possibly, somewhat in the etch stop layer405, as is also depicted in FIG. 4D. However, where a SiGe layer 405 isused at least a portion remains unoxidized, protecting semiconductorbodies 406 from oxidation. Referring to FIG. 4E, the spacers andhardmask are removed to leave isolation pedestals 422, etch stop layer405 and semiconductor bodies 406 remaining. Focusing the remainder ofthe description on only one semiconductor body 406, a dielectric pattern430 may be formed to surround the semiconductor body 406 and isolationpedestal 422, as depicted in FIG. 4F, e.g., an inter-layer dielectric(ILD) pattern. Referring to FIG. 4G, portions of the etch stop layer 405are selectively removed to provide an entirely exposed portion 432 ofthe semiconductor body 406 above isolation pedestal 422. For example, inone embodiment, the portion of the etch stop layer 405 under the channelregion of the semiconductor body 406 is removed, e.g., to ultimatelyenable formation of a gate-all-around structure. In another embodiment,the portions of the etch stop layer 405 under the source/drain regionsof the semiconductor body 406 are removed, e.g., to ultimately enableformation of a contact-all-around structure. In another embodiment, atdifferent stages in a process flow, the portion of the etch stop layer405 under the channel region of the semiconductor body 406 is removedand the portions of the etch stop layer 405 under the source/drainregions of the semiconductor body 406 are removed, e.g., to ultimatelyenable formation of a gate-all-around and a contact-all-aroundstructure. Using the first case as an example, a gate stack 440 isformed within the structure of FIG. 4G to provide a gate-all-aroundstructure 440, as depicted in FIG. 4H. The gate stack 440 includes agate dielectric layer 442 and a gate electrode 444 material surroundingthe channel region 432 of the semiconductor body 406. Referring to FIGS.4E and 4I (note that FIG. 4I is a view taken perpendicularly from FIG.4H), before or after the gate formation, epitaxial source and drainregions 460 are formed. In one such embodiment, source and drain regionsof the semiconductor body 406 are removed, using corresponding portionof the etch stop layer 405 for selective etching, and epitaxial sourceand drain regions are formed. Subsequently, as depicted in FIG. 4I, theportions of the etch stop layer 405 under the epitaxial source and drain460 are removed to enable a contact-all-around structure. Referring toFIG. 4J, in the case that the gate stack 440 is not permanent, the gatestack may be replaced with a permanent gate stack 470, such as a high-kmetal gate stack.

It is to be understood that following FIG. 4E above, differentcombinations of the operations shown in FIGS. 4F-4I may be selected forprocessing. For example, the source and drain regions of semiconductorbody 406 need not be replaced with epitaxial regions. Also, the portionsof the etch stop layer under regions 460 need not be removed.Additionally, referring to FIG. 4I as an example, artifacts fromprocessing may remain. As an example, regions 405A of the etch stoplayer 405 may remain underneath gate electrode spacers 465. Overall, ina general embodiment however, FIGS. 4A-4J illustrate an exemplaryprocess flow in which a sacrificial SiGe layer is used at the bottom ofa fin structure only.

Referring again to FIG. 4D, in an embodiment, the exposed portions ofthe semiconductor pedestals 420 are oxidized to form the isolationpedestals 422 by “under fin oxidation” (UFO). In an embodiment, the useof spacers may be required if a same or like material is being oxidized,and may even be included if non-like materials are used. In anembodiment, an oxidizing atmosphere or an adjacent oxidizing materialmay be used for UFO. However, in another embodiment, oxygen implant isused. In some embodiments, a portion of a material is recessed prior toUFO which may reduce the extent of so-called birds-beak formation duringoxidation. Thus, the oxidation may be performed directly, by recessingfirst, or by oxygen implant, or a combination thereof. In anotherembodiment, in place of UFO, selective removal of a material at thebottom of the fin (e.g., a material that has been previously depositedon the silicon wafer before an additional fin material deposition, suchas silicon germanium on a silicon substrate) is performed and replacedwith a dielectric material, such as silicon dioxide or silicon nitride.In either the UFO case or the selective material removal case, thelocation where reoxidation or material replacement is performed canvary. For example, in one such embodiment, the reoxidation or materialremoval is carried out post gate etch, post spacer etch, at an undercutlocation, at a replacement gate operation, or at a through contactoperation, or a combination thereof.

Referring again to FIG. 4G, in an embodiment, a portion of the silicongermanium etch stop layer 405 is etched selectively with a wet etch thatselectively removes the silicon germanium etch stop layer 405 portionwhile not etching the silicon body 406. Etch chemistries such ascarboxylic acid/nitric acid/HF chemistry, and citric acid/nitricacid/HF, for example, may be utilized to selectively etch the silicongermanium. In another embodiment, a silicon etch stop layer is usedbelow a silicon germanium body. Etch chemistries such as aqueoushydroxide chemistries, including ammonium hydroxide and potassiumhydroxide, for example, may be utilized to selectively etch the silicon.Thus, either a silicon layer may be removed from a silicon germaniumfin-type structure or a silicon germanium layer may be removed from asilicon fin-type structure.

Referring again to FIGS. 4F-4J, gate stack structures may be fabricatedby a replacement gate process. In such a scheme, dummy gate materialsuch as polysilicon or silicon nitride pillar material, may be removedand replaced with permanent gate electrode material. In one suchembodiment, a permanent gate dielectric layer is also formed in thisprocess, as opposed to being carried through from earlier processing. Inan embodiment, dummy gates are removed by a dry etch or wet etchprocess. In one embodiment, dummy gates are composed of polycrystallinesilicon or amorphous silicon and are removed with a dry etch processcomprising SF₆. In another embodiment, dummy gates are composed ofpolycrystalline silicon or amorphous silicon and are removed with a wetetch process comprising aqueous NH₄OH or tetramethylammonium hydroxide.In one embodiment, dummy gates are composed of silicon nitride and areremoved with a wet etch including aqueous phosphoric acid.

In a second example utilizing a UFO approach, FIGS. 5A-5J illustratecross-sectional views of various operations in another method offabricating a semiconductor device, in accordance with an embodiment ofthe present invention. Referring to FIG. 5A, a starting semiconductorstructure 500 includes semiconductor bodies 506, such as silicon fins,disposed on an undercut etch stop layer 505A, such as a silicongermanium etch stop layer. The undercut etch stop layer 505A is disposedon a substrate 502, such as a bulk silicon substrate. A second etch stoplayer 505B, such as a second silicon germanium etch stop layer, isdisposed on the semiconductor bodies 506. A hardmask layer 510, such asa silicon nitride hardmask layer, is disposed on the second etch stoplayer 505B. Spacers 512, such as silicon nitride spacers are formedalong the sidewalls of the semiconductor bodies 506, as depicted in FIG.5B, e.g., by conformal layer deposition and etch back. Referring to FIG.5C, exposed portions of the substrate 502 are removed to providesemiconductor pedestals 520 underneath the semiconductor bodies 506. Forexample, in the case that the semiconductor bodies 506 are protected bysilicon nitride hardmask and spacers and by a silicon germanium etchstop layer 505A, the semiconductor pedestals 520 may be formedselectively without impacting the semiconductor bodies 506. Thesemiconductor pedestals 520 are then oxidized to form isolationpedestals 522, as depicted in FIG. 5D. Oxidation may also occur in thetop portion of the remaining substrate 502 and, possibly, somewhat inthe etch stop layer 505A, as is also depicted in FIG. 5D. However, wherea SiGe layer 505A is used at least a portion remains unoxidized,protecting semiconductor bodies 506 from oxidation. Referring to FIG.5E, the spacers and hardmask are removed to leave isolation pedestals522, etch stop layers 505A and 505B and semiconductor bodies 506remaining. Focusing the remainder of the description on only onesemiconductor body 506, a dielectric pattern 530 may be formed tosurround the semiconductor body 506 and isolation pedestal 522, asdepicted in FIG. 5F, e.g., an inter-layer dielectric (ILD) pattern.Referring to FIG. 5G, portions of the etch stop layers 505A and 505B areselectively removed to provide an entirely exposed portion 532 of thesemiconductor body 506 above isolation pedestal 522. For example, in oneembodiment, the portions of the etch stop layers 505A and 505B under andabove the channel region of the semiconductor body 506 are removed,e.g., to ultimately enable formation of a gate-all-around structure. Inanother embodiment, the portions of the etch stop layers 505A and 505Bunder and above the source/drain regions of the semiconductor body 506are removed, e.g., to ultimately enable formation of acontact-all-around structure. In another embodiment, at different stagesin a process flow, the portion of the etch stop layers 505A and 505Bunder and above the channel region of the semiconductor body 506 areremoved and the portions of the etch stop layers 505A and 505B under andabove the source/drain regions of the semiconductor body 506 areremoved, e.g., to ultimately enable formation of a gate-all-around and acontact-all-around structure. Using the first case as an example, a gatestack 540 is formed within the structure of FIG. 5G to provide agate-all-around structure 550, as depicted in FIG. 5H. The gate stack540 includes a gate dielectric layer 542 and a gate electrode 544material surrounding the channel region 532 of the semiconductor body506. Referring to FIGS. 5E and 5I (note that FIG. 5I is a view takenperpendicularly from FIG. 5H), before or after the gate formation,epitaxial source and drain regions 560 are formed. In one suchembodiment, source and drain regions of the semiconductor body 506 areremoved, using corresponding portion of the etch stop layer 505A forselective etching, and epitaxial source and drain regions are formed.Subsequently, as depicted in FIG. 5I, the portions of the etch stoplayer 505A under the epitaxial source and drain 560 are removed toenable a contact-all-around structure. Referring to FIG. 5I, in the casethat the gate stack 540 is not permanent, the gate stack may be replacedwith a permanent gate stack 570, such as a high-k metal gate stack.

It is to be understood that following FIG. 5E above, differentcombinations of the operations shown in FIGS. 5F-5I may be selected forprocessing. For example, the source and drain regions of semiconductorbody 506 need not be replaced with epitaxial regions. Also, the portionsof the etch stop layer under regions 560 need not be removed.Additionally, referring to FIG. 5I as an example, artifacts fromprocessing may remain. As an example, regions 505A′ and 505B′ of theetch stop layers 505A and 505B, respectively, may remain underneath gateelectrode spacers 565. Overall, in a general embodiment however, FIGS.5A-5J illustrate an exemplary process flow in which a sacrificial SiGelayer is used at the bottom and the top of a fin structure.

In an example utilizing already-formed buried oxide approach, FIGS.6A-6G illustrate cross-sectional views of various operations in anothermethod of fabricating a semiconductor device, in accordance with anembodiment of the present invention. Referring to FIG. 6A, a startingsemiconductor structure 600 includes semiconductor bodies 606, such assilicon fins, disposed on an undercut etch stop layer 605, such as asilicon germanium etch stop layer. The undercut etch stop layer 605 isdisposed on an insulating layer 604, such as a buried SiO₂ layer of asilicon-on-insulator (SOI) substrate. The insulating layer 604 isdisposed on a substrate 602, such as a silicon substrate. A hardmasklayer 610, such as a silicon nitride hardmask layer, is disposed on thesemiconductor bodies 606. The undercut etch stop layer 605 is patternedto expose insulating layer 604, as depicted in FIG. 6B, e.g., by a dryetch process. Focusing the remainder of the description on only onesemiconductor body 606, the hardmask 610 is removed and a dielectricpattern 630 is formed to surround the semiconductor body 606 andundercut etch stop layer 605, as depicted in FIG. 6C, e.g., aninter-layer dielectric (ILD) pattern. Although not depicted in FIG. 6C,source and drain undercut (e.g., as described in association with FIGS.2A-2C) and a replacement gate process may also be performed at, prior toor after, this stage. Referring to FIG. 6D, the bottom sacrificial layer(and top if present, such as described in association with FIGS. 5A-5J)is removed. Then, a gate dielectric layer 642 and metal gate electrode644 may be formed, as depicted in FIG. 6E. Referring to FIGS. 6F and 6G(latter is repeat of FIG. 6E), respectively, a comparison between theFIN cut 680 and poly cut 690 views is provided. In the former view, thepossibility to fabricate a trench contact wrap-around is available inthe source and drain regions.

It is to be understood that additional wire structures (such as thosedescribed in association with FIGS. 3A-3C) may also be fabricated inassociation with the fin structures described and illustrated in FIGS.4A-4J, 5A-5-J and 6A-6G above.

One or more embodiments described herein can be implemented improveperformance on, e.g., 14 nanometer and smaller node products and reducestandby leakage. Standby leakage reduction may be particularly importantfor system-on-chip (SOC) products with extremely stringent standby powerrequirements. Furthermore, other or the same embodiments may takeadvantage of higher mobility properties of strained channel engineeringusing SiGe or Ge as S/D stressors as an example. Also, thegate-all-around and/or contact-all-around structures are expected toimprove short channel performance and transistor contact resistance.

One or more embodiments of the present invention are directed atimproving the channel mobility for NMOS or PMOS transistors, or both.Mobility may be improved using strain, e.g., in the channel region.Thus, one or more approaches described herein provide the appropriatestrain in the channel regions for both NMOS and PMOS transistors. In anembodiment, strained NMOS and PMOS gate-all-around devices are provided.

More specifically, one or more embodiments of the present inventioninclude compressive strain for improved hole mobility for PMOSnanowire-based devices and tensile strain for improved electron mobilityfor NMOS nanowire-based devices. In an embodiment, strained silicon andstrained silicon germanium devices are formed from such layers in orderto improve or maximize device performance. In an embodiment, NMOS andPMOS uniaxially strained nanowire or nanoribbon devices are fabricatedon or above a common substrate by one or more approaches describedabove. The PMOS transistors may include SiGe having uniaxial compressivestrain along the current flow direction, while the NMOS transistors mayinclude silicon having uniaxial tensile strain along the current flowdirection.

FIG. 7 illustrates a computing device 700 in accordance with oneimplementation of the invention. The computing device 700 houses a board702. The board 702 may include a number of components, including but notlimited to a processor 704 and at least one communication chip 706. Theprocessor 704 is physically and electrically coupled to the board 702.In some implementations the at least one communication chip 706 is alsophysically and electrically coupled to the board 702. In furtherimplementations, the communication chip 706 is part of the processor704.

Depending on its applications, computing device 700 may include othercomponents that may or may not be physically and electrically coupled tothe board 702. These other components include, but are not limited to,volatile memory (e.g., DRAM), non-volatile memory (e.g., ROM), flashmemory, a graphics processor, a digital signal processor, a cryptoprocessor, a chipset, an antenna, a display, a touchscreen display, atouchscreen controller, a battery, an audio codec, a video codec, apower amplifier, a global positioning system (GPS) device, a compass, anaccelerometer, a gyroscope, a speaker, a camera, and a mass storagedevice (such as hard disk drive, compact disk (CD), digital versatiledisk (DVD), and so forth).

The communication chip 706 enables wireless communications for thetransfer of data to and from the computing device 700. The term“wireless” and its derivatives may be used to describe circuits,devices, systems, methods, techniques, communications channels, etc.,that may communicate data through the use of modulated electromagneticradiation through a non-solid medium. The term does not imply that theassociated devices do not contain any wires, although in someembodiments they might not. The communication chip 706 may implement anyof a number of wireless standards or protocols, including but notlimited to Wi-Fi (IEEE 802.11 family), WiMAX (IEEE 802.16 family), IEEE802.20, long term evolution (LTE), Ev-DO, HSPA+, HSDPA+, HSUPA+, EDGE,GSM, GPRS, CDMA, TDMA, DECT, Bluetooth, derivatives thereof, as well asany other wireless protocols that are designated as 3G, 4G, 5G, andbeyond. The computing device 700 may include a plurality ofcommunication chips 706. For instance, a first communication chip 706may be dedicated to shorter range wireless communications such as Wi-Fiand Bluetooth and a second communication chip 706 may be dedicated tolonger range wireless communications such as GPS, EDGE, GPRS, CDMA,WiMAX, LTE, Ev-DO, and others.

The processor 704 of the computing device 700 includes an integratedcircuit die packaged within the processor 704. In some implementationsof the invention, the integrated circuit die of the processor includesone or more devices, such as MOS-FET transistors built in accordancewith implementations of the invention. The term “processor” may refer toany device or portion of a device that processes electronic data fromregisters and/or memory to transform that electronic data into otherelectronic data that may be stored in registers and/or memory.

The communication chip 706 also includes an integrated circuit diepackaged within the communication chip 706. In accordance with anotherimplementation of the invention, the integrated circuit die of thecommunication chip includes one or more devices, such as MOS-FETtransistors built in accordance with implementations of the invention.

In further implementations, another component housed within thecomputing device 700 may contain an integrated circuit die that includesone or more devices, such as MOS-FET transistors built in accordancewith implementations of the invention.

In various implementations, the computing device 700 may be a laptop, anetbook, a notebook, an ultrabook, a smartphone, a tablet, a personaldigital assistant (PDA), an ultra mobile PC, a mobile phone, a desktopcomputer, a server, a printer, a scanner, a monitor, a set-top box, anentertainment control unit, a digital camera, a portable music player,or a digital video recorder. In further implementations, the computingdevice 700 may be any other electronic device that processes data.

Thus, embodiments of the present invention include strainedgate-all-around semiconductor devices formed on globally or locallyisolated substrates.

In an embodiment, a semiconductor device includes a semiconductorsubstrate. An insulating structure is disposed above the semiconductorsubstrate. A three-dimensional channel region is disposed above theinsulating structure. Source and drain regions are disposed on eitherside of the three-dimensional channel region and on an epitaxial seedlayer. The epitaxial seed layer is composed of a semiconductor materialdifferent from the three-dimensional channel region and disposed on theinsulating structure. A gate electrode stack surrounds thethree-dimensional channel region with a portion disposed on theinsulating structure and laterally adjacent to the epitaxial seed layer.

In one embodiment, the insulating structure is a global insulatinglayer.

In one embodiment, the insulating structure includes one or moreisolation pedestals.

In one embodiment, the three-dimensional channel region is composed ofsilicon, and the epitaxial seed layer is composed of silicon germanium.

In one embodiment, the source and drain regions are composed of silicongermanium and provide a uniaxial stress to the three-dimensional channelregion.

In one embodiment, the semiconductor structure further includes a pairof insulating spacers. One spacer is disposed between the gate electrodeand the source region. The other spacer is disposed between the gateelectrode and the drain region. The epitaxial seed layer extendsunderneath each of the pair of spacers.

In one embodiment, the semiconductor structure further includes a pairof conducting contacts. One contact is disposed on and partiallysurrounds the source region. The other contact is disposed on andpartially surrounds the drain region.

In one embodiment, the semiconductor structure further includes one ormore nanowires disposed in a vertical arrangement above thethree-dimensional channel region. The gate electrode stack surrounds achannel region of each of the one or more nanowires. In one embodiment,the gate electrode stack is composed of a high-k gate dielectric layerand a metal gate electrode.

In an embodiment, a semiconductor device includes a semiconductorsubstrate. An insulating structure is disposed above the semiconductorsubstrate. A three-dimensional channel region is disposed on anepitaxial seed layer disposed on the insulating structure. The epitaxialseed layer is composed of a semiconductor material different from thethree-dimensional channel region. A gate electrode stack partiallysurrounds the three-dimensional channel region. Source and drain regionsare disposed on either side of the three-dimensional channel region andabove the insulating structure. A pair of conducting contacts isincluded, one contact disposed on and surrounding the source region, andthe other contact disposed on and surrounding the drain region. Aportion of each of the pair of contacts is disposed on the insulatingstructure and laterally adjacent to the epitaxial seed layer.

In one embodiment, the insulating structure includes a global insulatinglayer.

In one embodiment, the insulating structure includes one or moreisolation pedestals.

In one embodiment, the three-dimensional channel region is composed ofsilicon, and the epitaxial seed layer is composed of silicon germanium.

In one embodiment, the source and drain regions are composed of silicongermanium and provide a uniaxial stress to the three-dimensional channelregion.

In one embodiment, the semiconductor structure further includes a pairof insulating spacers. One spacer is disposed between the gate electrodeand the source region. The other spacer is disposed between the gateelectrode and the drain region. The epitaxial seed layer extendsunderneath each of the pair of spacers.

In one embodiment, the semiconductor structure further includes one ormore nanowires disposed in a vertical arrangement above thethree-dimensional channel region. The gate electrode stack surrounds achannel region of each of the one or more nanowires.

In one embodiment, the gate electrode stack includes a high-k gatedielectric layer and a metal gate electrode.

In an embodiment, a semiconductor device includes a semiconductorsubstrate. An insulating structure is disposed above the semiconductorsubstrate. A three-dimensional channel region is disposed above theinsulating structure. A gate electrode stack surrounds thethree-dimensional channel region with a portion disposed on theinsulating structure. Source and drain regions are disposed on eitherside of the three-dimensional channel region and above the insulatingstructure. A pair of conducting contacts is included, one contactdisposed on and surrounding the source region, and the other contactdisposed on and surrounding the drain region. A portion of each of thepair of contacts is disposed on the insulating structure. A pair ofinsulating spacers is included, one spacer disposed between the gateelectrode and the source region, and the other spacer disposed betweenthe gate electrode and the drain region. A remnant of an epitaxial seedlayer is disposed underneath each of the pair of spacers and laterallyadjacent to a portion of the gate electrode stack and a portion of eachof the conducting contacts. The remnant of the epitaxial seed layer iscomposed of a semiconductor material different from thethree-dimensional channel region.

In one embodiment, the insulating structure includes a global insulatinglayer.

In one embodiment, the insulating structure includes one or moreisolation pedestals.

In one embodiment, the three-dimensional channel region is composed ofsilicon, and the remnant of the epitaxial seed layer is composed ofsilicon germanium.

In one embodiment, the source and drain regions are composed of silicongermanium and provide a uniaxial stress to the three-dimensional channelregion.

In one embodiment, the semiconductor structure further includes one ormore nanowires disposed in a vertical arrangement above thethree-dimensional channel region. The gate electrode stack surrounds achannel region of each of the one or more nanowires.

In one embodiment, the gate electrode stack includes a high-k gatedielectric layer and a metal gate electrode.

In an embodiment, a method of fabricating a semiconductor deviceincludes forming a three-dimensional semiconductor structure on anepitaxial seed layer disposed above a semiconductor substrate. Theepitaxial seed layer is composed of a semiconductor material differentfrom the three-dimensional semiconductor structure. Thethree-dimensional semiconductor structure is etched to provide athree-dimensional channel region and to expose portions of the epitaxialseed layer on either side of the three-dimensional channel region.Source and drain regions are formed on either side of thethree-dimensional channel region and on an epitaxial seed layer. Thethree-dimensional channel region and the source and drain regions areinsulated from the semiconductor substrate. Subsequently, a portion ofthe epitaxial seed layer is removed. A gate electrode stack is formed atleast partially surrounding the three-dimensional channel region. A pairof conducting contacts is formed, one contact at least partiallysurrounding the source region, and the other contact at least partiallysurrounding the drain region.

In one embodiment, insulating the three-dimensional channel region andthe source and drain regions includes providing a global insulatinglayer on the semiconductor substrate.

In one embodiment, insulating the three-dimensional channel region andthe source and drain regions includes forming one or more isolationpedestals.

In one embodiment, forming the gate electrode stack includes using areplacement gate process.

In one embodiment, removing the portion of the epitaxial seed layerincludes removing a portion between the three-dimensional channel regionand the semiconductor substrate. The gate electrode stack surrounds thethree-dimensional channel region.

In one embodiment, removing the portion of the epitaxial seed layerincludes removing a portion between the source and drain regions and thesemiconductor substrate. The one contact surrounds the source region andthe other contact surrounds the drain region.

What is claimed is:
 1. A method of fabricating a semiconductor device,the method comprising: forming a three-dimensional semiconductorstructure on an epitaxial seed layer disposed above a semiconductorsubstrate, the epitaxial seed layer comprising a semiconductor materialdifferent from the three-dimensional semiconductor structure; etchingthe three-dimensional semiconductor structure to provide athree-dimensional channel region and to expose portions of the epitaxialseed layer on either side of the three-dimensional channel region;forming source and drain regions on either side of the three-dimensionalchannel region and on the epitaxial seed layer; insulating thethree-dimensional channel region and the source and drain regions fromthe semiconductor substrate by forming an insulating structurecomprising one or more isolation pedestals, the insulating structurecontinuous with the semiconductor substrate; and, subsequently, removinga portion of the epitaxial seed layer; forming a gate electrode stack atleast partially surrounding the three-dimensional channel region; andforming a pair of conducting contacts, one contact at least partiallysurrounding the source region, and another contact at least partiallysurrounding the drain region, wherein removing the portion of theepitaxial seed layer comprises removing a portion between the source anddrain regions and the semiconductor substrate, and wherein the onecontact surrounds the source region and the other contact surrounds thedrain region.
 2. The method of claim 1, wherein forming the gateelectrode stack comprises using a replacement gate process.
 3. Themethod of claim 1, wherein removing the portion of the epitaxial seedlayer further comprises removing a portion between the three-dimensionalchannel region and the semiconductor substrate, and wherein the gateelectrode stack surrounds the three-dimensional channel region.
 4. Amethod of fabricating a semiconductor device, the method comprising:forming a three-dimensional semiconductor structure on an epitaxial seedlayer disposed above a semiconductor substrate, the epitaxial seed layercomprising a semiconductor material different from the three-dimensionalsemiconductor structure; etching the three-dimensional semiconductorstructure to provide a three-dimensional channel region and to exposeportions of the epitaxial seed layer on either side of thethree-dimensional channel region; forming source and drain regions oneither side of the three-dimensional channel region and on the epitaxialseed layer; insulating the three-dimensional channel region and thesource and drain regions from the semiconductor substrate by forming aninsulating structure comprising one or more isolation pedestals, theinsulating structure continuous with the semiconductor substrate;removing a portion of the epitaxial seed layer; forming a gate electrodestack at least partially surrounding the three-dimensional channelregion; and forming a pair of conducting contacts, one contact at leastpartially surrounding the source region, and another contact at leastpartially surrounding the drain region, wherein removing the portion ofthe epitaxial seed layer comprises removing a portion between the sourceand drain regions and the semiconductor substrate, and wherein the onecontact surrounds the source region and the other contact surrounds thedrain region.
 5. The method of claim 4, wherein forming the gateelectrode stack comprises using a replacement gate process.
 6. Themethod of claim 4, wherein removing the portion of the epitaxial seedlayer further comprises removing a portion between the three-dimensionalchannel region and the semiconductor substrate, and wherein the gateelectrode stack surrounds the three-dimensional channel region.